Various types of storage structures are used for storage of gases, liquids and solids as well as in the processing of such materials. Such structures vary widely in shape and size. They can have planar surfaces, single curved surfaces such as a cylindrical surface, a double curved surface such as a spheroidal surface, and combinations of such curved surfaces. Some specific storage structures having such surfaces are cylindrical circular storage tanks having flat, conical or domed roofs and which are used extensively for petroleum product storage, water storage and ice-water slurry storage, liquefied gas storage, elevated water storage tanks including those which have a spheroidal-shaped tank supported on a single column, cylindrical water storage tanks supported on a single column, elevated tanks of various curved shapes supported by a plurality of columns or by a cylindrical vertical wall, and various storage and processing vessels of spherical shape. Such storage structures are generally made of metal plate or concrete.
Because the internal temperature of many storage structures in use is significantly, or appreciably, higher or lower than the surrounding environmental or atmospheric temperature it is desirable, and often necessary, to insulate part or all of the storage structures to retard heat transfer through the walls of the storage structures and, at times, to restrict the passage of water vapor into the insulation and/or the condensation of water on the walls beneath the insulation.
Various types of insulation have been applied to storage structures for the stated purposes. Thus, Davis et. al. U.S. Pat. No. 3,878,658 shows a system using layers of insulating board applied to a tank. Garis U.S. Pat. No. 3,548,453 and Larsen U.S. Pat. No. 3,991,842 disclose applying polyurethane foam directly onto tanks with the contemporaneous application of a metal sheet over the insulation to protect it against the weather and the penetration of water into the insulation and then to the tank wall.
While the described insulation systems serve their functional purpose often they do not radiate the architectural quality and appearance which customers desire, especially when the structures are located amongst institutional, commercial, government and residential buildings or in parks and athletic facilities. The surfaces after insulation do not have significant depth in that they lack grooves, bas-relief designs and other sculptured features and textures as would commonly be found in architectural practice.
At the present time some commercial and government buildings have exterior walls built-up in layered arrangement so as to provide thermal insulation and a pleasing exterior finish which weathers well. The exterior walls are built-up by first applying insulating board to the building substrate which, for example, may be concrete, building blocks, gypsum board and metal lath. The insulating board is held in place by mechanical fasteners or an adhesive. Then the outer surface of the insulating board, which can be rigid expanded polystyrene, is coated with a layer of synthetic stucco in which a glass fiber fabric mesh is embedded for reinforcement followed by a finish layer of synthetic stucco. The adhesive and the stucco material can be polyacrylic latex products such as those marketed by Dryvit Systems, Inc., West Warwick, R.I. Whatever vapor barrier is needed in such buildings is placed on the interior of the building, behind the inner wall as is conventional for buildings intended for habitation by humans. A polyethylene film behind the inside wall is often used as a vapor barrier to keep moisture from driving into an air conditioned building. Normally there is no vapor barrier behind or inside the outer wall of the building so that moisture can flow out of the building in the winter and not freeze and cause damage to the building.
While the described built-up layered exterior walls perform well on buildings of the types described above they cannot be applied with confidence to storage structures such as tanks because water vapor can penetrate such walls and condense on the exterior surface of the storage structure causing corrosion problems for a metal tank or for the metal reinforcement of a concrete tank, a serious loss in insulating capacity, weakening of the insulation or causing it to loosen.
It was contemplated that all one had to do to prevent vapor flow through the exterior wall was to apply a layer of conventional material used previously as a vapor barrier to seal the exterior surface or the insulation layer. However, placement of the vapor barrier coating on top of the exterior finish would largely or totally defeat the intended effect of the architectural finish. Also, conventional vapor barrier coatings, such as butyl rubber, are solvent-based and thus unacceptable as an intermediate layer due to their incompatibility with many insulation compositions, and specifically foamed polystyrene. Furthermore, prior to our discovery, no vapor barrier composition was known which could be successfully used in a built-up wall of the previously described type, either because it was incompatible with the insulation or the synthetic stucco. In addition, it was not known whether a vapor barrier layer and a stucco layer could be applied successfully in contact with, or adjacent one another, in a built-up finish covering for a storage structure wall.